1

CHAPTER III

MECHANICAL DESIGN OF EQUIPMENT

3.1 REACTOR 1, R1

3.1.1 INTRODUCTION
In the mechanical design of process equipment, there are many aspects of
design and reactor safety factors should be considered. Among these is the stress
analysis, the burdens imposed on the reactor and the reactor design supporters. All
these aspects are based on a standard code of the American Society of Mechanical
Engineers (ASME).
Tube and shell reactor was operated in the gas phase and liquid phase at a
temperature of 185
0
C and pressure of 6.5 bar (650 kPa) design pressure, P took a
safety factor of 10% above the operating pressure.

3.1.2 MATERIAL OF CONSTRUCTION

Materials selection was based on the consideration of four main factors:
resistance to ammonia, nitric acid and ammonium nitrate vapours and condensate,
strength, ease of fabrication, and low cost. Much of the vessel (both the shell and
the tubes) will be in continuous contact with ammonium nitrate aqueous at high
temperatures. Therefore, particular attention was given to corrosion resistance
under those conditions. The tubes are in direct contact with both the cooling medium
and the reaction gases.
The preferred construction material for the reactor is stainless steel 16Cr-
2Mo-8Ni (316), which is described by the materials specification given in Table 5.2
and composition of material in Table 5.3. Ammonium nitrate, ammonia and nitric
acid are not particularly corrosive to most steels. The average corrosion rates are
generally less than 0.001 per year. The addition of chromium also improves the
mechanical properties at high temperature. Several stainless steels, notably type
316, satisfy all the material requirements. However, A387 is substantially cheaper
and can be used with little penalty to the corrosion rate. At high pressures (and,
2

hence, large wall thicknesses), cladding is normally recommended in order to
reduce the vessel cost when alloy steels are used.
Reactor construction material used is stainless steel 16Cr-2Mo-8Ni (316). By
referring to the standard code The American Society of Mechanical Engineers
(ASME), the maximum stress is 133.5 N/mm
2
.

3.1.3 THE EFFICIENCY OF WELDED JOINT
There are several methods to make welded joints. In particular case the
choices of a type from the numerous alternatives depend on:
1. The circumstances of welding.
In many cases the accessibility of the joint determines the types of welding.
In a small diameter vessel (under 18-24 inches) from the inside, no manual welding
can be applied. Using backing strip it must remain in place. In larger diameter
vessels if a manway is not used, the last (closing) joint can be welded from outside
only. The type of welding may be determined also by the equipment of the
manufacturer.
2. The requirements of the code.
Regarding the type of joint the Code establishes requirements based on
service, material and location of the welding. The welding processes that may be
used in the construction of vessels are also restricted by the Code as described in
paragraphUW-27.
3. The aspect economy.
If the two preceding factors allow free choice, then the aspect of economy
must be the deciding factor.
Some considerations concerning the economy of welding’s:
1. V-edge preparation, which can be made by torch cutting, is always more
econornical than the use of J or U preparation.
2. Double V preparation requires only half the deposited weld metal required for
single V preparation.
3. Increasing the size of fillet weld, its strength increases in direct proportion,
while the deposited weld metal increases with the square of its size.
4. Lower quality welding makes necessary the use of thicker plate for the
vessel. Whether using stronger welding and thinner plate or the opposite is
more economical, depends on the size of vessel, welding equipment, etc.
This must be decided in each particular case
The strength of a welded joint depends on the type and quality of welding
joint. Then, for design purposes weld joint efficiency, J = 1.0 was chosen. This
selection is based on ASME UW-2 stated that:
4

“… all butt welded joints shall be fully radiographe, except under provision
OS UW-2(a)(2) and UW-2(a)(3) below and UW-4(a)(4)….”
This statement is clarifying the requirement of welded joint that fully
radiograph when pressure vessel containing lethal substances. So, all main
category A and B welds must be fully radiographed. But category B and C welds in a
nozzle and communicating chambers that are not larger than 10 inch nominal pipe
size and do not exceed 1to 1/8 inch thick are exempt. Based on the fluid
composition contain in the reactor for this design, ammonium nitrate could be a
dangerous and lethal substance if leaking to the atmosphere. Furthermore,
ammonia also potentially dangerous substance. The location of A, B and C shown in
Figure 5.3.

The pressure given in the table only design stress for selected material but
for design stress pressure that generated by the fluid also need to take into
consideration. From book of Pressure Vessel Handbook 10
th
edition page 29 giving
5

the pressure of water that will emit at different length. But for other material, the
value needs to multiply with specific gravity of fluid or other calculation is:

Value above is for the water. To get the pressure in the reactor emit by the
fluid is multiply value get by specific gravity of fluid. Specific gravity for the fluid in
the reactor is 0.1067.

This shows the inefficiency of a flat cover. It would be better to use a
flanged domed head. So, ellipsoidal head will be used as domed head for reactor.

8

3.1.4.5 Tube sheet (plate)
Tube sheet forms the barrier between shell and tube fluids, and where it is
essential for safety or process reason to prevent any possibility of intermixing due to
leakage at the tube sheet joint, double tube-sheets can be used, with the space
between the sheet vented. The thickness of tube sheet will reduce the effective
length of the tube slightly, and this should be allowed for when calculating the area
available for heat transfer. The thickness of tube sheet calculation given by the
TEMA standard as below
Thickness of tube sheet

Where

and

Where

= Outlet diameter of shell, mm

= Outlet diameter of tube, mm

= Number of tube

= Thickness of tube, mm

= Thickness of shell, mm
= Design pressure, N/mm
2

= Design stress, N/mm
2

= Elastic modulus of shell, N/mm
2

= Elastic modulus of tube, N/mm
2

Therefore, from equation 5.49

Substituted k value into equation 5.48

Substituted F value inside equation 5.47
9

3.1.4.6 Reactor load
3.1.4.6.1 Weight of a cylindrical vessel with domed end

Where
W
v
= total weight of the shell, excluding internal fittings, such as plates, N,
C
v
= a factor to account for the weight of nozzles, man ways, internal supports,
etc; which can be taken as
= 1.08 for vessels with only a few internal fittings,
= 1.15 for distillation columns, or similar vessels, with several man ways,
and with plate support rings, or equivalent fittings,
H
v
= height, or length, between tangent lines (the length of the cylindrical
section) = 15 m
g = gravitational acceleration, 9.81 m/s
2
,
t = wall thickness = 18.0 mm
p
m
= density of vessel material = 7787 kg/m3,
D
m
= mean diameter of vessel D =4.818 m.
C
v
taken is 1.08 for a few internal fittings.
Therefore, from equation 5.47

3.1.4.7.2 Direct stress
Direct stress is the stress that generated by the fluid inside vessel and its
vessel weight

Where

= Total weight of reactor (shell), kN

= Inside diameter, m

= Thickness of shell, m
Therefore, from equation 5.58

3.1.4.8 Support
Support saddle used to support the container in a horizontal reactor. The
former is supported by two saddles can be considered as a simple supported beam
with uniformly distributed load. The distribution of the longitudinal axis of the bending
moment is shown in the diagram below:

13

The maximum point occurs on both sides and support the middle range. In
theory, the optimum support position, giving rise to the maximum bending moment is
the lowest position when the magnitude of the maximum value on both sides is
equal to the value of support in the middle of the range of:

1 2
2
L L
M M =

Where
A = Distance from the tangent to the saddle support, m
L = Length of the container, the tangent line, m
H = column depth, m
= 1.218 m
Q = Total weight/saddle, N
= Total weight/2
= 1144.6171 kN
R = Radius of reactor
= 2.4 m
b = width of saddle, m
Bending moments at the two saddle supports, and bending in the middle of
the range, can be determined using the following equations:

14

Balance from the bending moment:

Solving from above equation, value for A =3.97m
Therefore

3.1.4.9 Stresses in vessel wall
Bending stress is a stress that cause by the bending moment in the shell
(vessel), bending moment is classified as the stress generated as a resultant to the
dead weight of reactor in horizontal position supported by the saddle support.
Bending stress longitudinal to the cross sectional area of shell as

The difference in principal stresses and the longitudinal stress resultant,

Because of the stress difference is <the maximum stress, S, the design is
acceptable.
The magnitude of the longitudinal bending stress on the strengthening of
support will depend on the local shell. If the shell does not remain round when
loaded, this means that some of the top cross section is not effective against
longitudinal bending. This stress is given as follows:

Where

= Longitudinal bending moment at the support

= an empirical constant: 1.0 for stiffened shell.
Therefore,

Because the value of o
b
, 2 is smaller than the maximum design stress
allowable S, then the pressure vessel design of the heat exchanger is acceptable.
16

3.1.4.10 Saddle design
Saddle must be designed to withstand heavy loads caused by the container
and its contents. This saddle is made of stainless steel plate. Typically, the contact
angle cannot be less than 120°and not more than 150
0
. Smooth plates (wear plate)
are usually welded to the shell wall to reinforce the wall area in contact with the
saddle.
Saddle support design procedure given by Brownell and Young (1959) and
Megyesy (1977), the former equal to the diameter of 4.86 m, standard steel saddles
to container with a diameter of 4.8 m is used after interpolation been made as
shown in Table 5.3.

3.1.4.11 Design bolt flange connection
Flange can be used in the body of the container when the container must
be divided into several sections for easy removal and maintenance. Flange
connection used to connect pipes to other equipment such as pumps and valves.
Typically used for connecting the connection of bolt with small diameter pipes, less
than 40 mm. Flange connections are also used to attach sections of pipe on the
installation and opening of facilities needed for maintenance, but the structure of the
pipe is usually welded to reduce costs.
Flange sizes vary, from a few millimeters in diameter for small pipes to
several meters in diameter for use as a body or head flange on the container. There
are four openings in the design of the reactor tube and shell, which requires the use
of connection, namely:
1. Welding-neck flanges.
2. Slip-on flanges, hub and plate types.
3. Lap-joint flanges.
4. Screwed flanges.
5. Blank, or blind, flanges.

Welded-neck flange type (steel) used for opening the input and output
openings for the connection and the nozzle of the reactor tube and shell. Given the
pressure vessel is operated under the operating pressure of 6.5 bar (650 kPa) at a
temperature of 155 °C design, the flange of this type is selected for its ability to
withstand extreme operating conditions likely to be exposed to temperature loading,
shear, and vibration.
Optimum size for the flange to the nozzles feed (input) and the output of the
shell and tube can be determined using the following equation proposed by Sinnot:

3.2.1 Design Pressure
A vessel must be designed to withstand the maximum pressure to which it
is likely to be subjected in operation. For vessels under internal pressure, the design
pressure is normally taken as the pressure at which the relief device is set. This will
normally be 5 to 10 per cent above the normal working pressure, to avoid spurious
operation during minor process upsets. In this design, considering 10 % safety
factor so that the design pressure become as below:

(1.36)

3.2.2 Design Temperature
The operating temperature of our reactor is taken as 185
0
C. For safety
reason, the design pressure of this reactor is taken as 10% above the operating
temperature to avoid spurious operation during minor process upsets.

(1.37)

0
C

K

3.2.3 Material Of Construction
Many factors have to be considered when selecting engineering materials
but for chemical process plant the overriding consideration is usually the ability to
resist corrosion. The material selected must have sufficient strength and be easily
worked. The most economical material that satisfies both process and mechanical
requirements should be selected which is this will be the material that gives the
lowest cost over the working life of the plant and allowing for maintenance and
replacement.
Stainless steels are the most frequently used corrosion resistant materials in
the chemical industry. To impart corrosion resistance the chromium content must be
above 12 per cent and the higher the chromium content, the more resistant is the
alloy to corrosion in oxidising conditions. Nickel is added to improve the corrosion
resistance in non-oxidising environments.
25

A wide range of stainless steels is available, with compositions tailored to
give the properties required for specific applications. Type 304 also-called 18/8
stainless steels is the most generally used stainless steel. It contains the minimum
Cr and Ni that give a stable austenitic structure. The carbon content is low enough
for heat treatment not to be normally needed with thin sections to prevent weld
decay. The uniform structure of austenitic is the structure desired for corrosion
resistance and it is these grades that are widely used in the chemical industry. The
austenitic stainless steels have greater strength than the plain carbon steels,
particularly at elevated temperatures (see Appendix A1). So, as conclusion stainless
steels type 304 is the best material of construction and then selected as material of
construction for the reactor.

The strength of metals decreases with increasing temperature, so the
maximum allowable design stress will depend on the material temperature. The
design temperature at which the design stress is evaluated should be taken as the
maximum working temperature of the material. With design temperature is equal to
maximum operating temperature, 185
o
C, design stress for stainless steel 304, is f =
115 N/mm
2
= 115 bar (R.K. Sinnot, 1999. Chemical Engineering Design). Typical
design stress values for some common materials are shown in Appendix A2.
Thus from Eqn. (1.38),

26

The corrosion allowance is the additional thickness of metal added to allow
for material lost by corrosion and erosion, or scaling. Corrosion is a complex
phenomenon and it is not possible to give specific rules for the estimation of the
corrosion allowance required for all circumstances. The allowance should be based
on experience with the material of construction under similar service conditions to
those for the proposed design. For carbon and low-alloy steels, where severe
corrosion is not expected, a minimum allowance of 2.0 mm should be used.

Add allowance for corrosion = + 0.002 m =

3.2.5 Design of Vessel Heads
The end of a cylindrical vessel is closed by heads of various shapes. The
common types used are:
i. Flat heads
ii. Hemispherical heads
iii. Ellipsoidal heads
iv. Torispherical heads

The heads used for the vessel may be flat if they are suitably buttressed
but preferably they are some curved shape as the hemispherical, ellipsoidal or
torispherical heads. Standard torispherical heads (dished ends) are the most
commonly used end closure for vessels up to operating pressures of 15 bar. They
can be used for higher pressures, but above 10 bar their cost should be compared
with that of an equivalent ellipsoidal head. Above 15 bar an ellipsoidal head will
usually prove to be the most economical closure to use.
The minimum thickness of torispherical and ellipsoidal head can be
calculated by using equation below:
For torispherical heads,

3.2.6 Determination of Piping Sizing
Liquids particularly can be transported through pipelines with pumps,
blowers, compressors or ejectors. Standard pipe is made in a discrete number of
sizes that are designed by nominal diameters (R.K. Sinnot, 1999. Chemical
Engineering Design).

3.2.7 Design Of Reactor Vessel Subject To Combined Loading
Pressure vessels are subjected to other loads in addition to pressure and
must be designed to withstand the worst combination of loading without failure. The
main sources of load to consider are:
i. Pressure
ii. Dead weight of vessel and contents
iii. External loads imposed by piping and attached equipments

iv. External fittings: ladders, platforms, piping.
v. The weight of liquid to fill the vessel. The vessel will be filled with
water for the hydraulic pressure test and may fill with process liquid
due to misoperation.
For preliminary calculations the approximate weight of a cylindrical vessel
with domed ends and uniform wall thickness, can be estimated from the following
equation:

(1.44)

Where,
Cv = a factor account for the weight of nozzles, man ways
= 1.08 for vessel with only a few internal fittings
= 1.15 for vessel with several man ways and other fittings

3.2.8 Vessel Support
The method used to support a vessel will depend on the size, shape and
weight of the vessel, the design temperature and pressure, the vessel location and
arrangement and the internal and external fittings and attachments. Horizontal
vessels are usually mounted on two saddle supports (see Appendix A4). The
supports must be designed to carry the weight of the vessel and contents, and any
superimposed loads, such as wind loads. Supports will impose localized loads on
the vessel wall and the design must be checked to ensure that the resulting stress
concentrations are below the maximum allowable design stress. Supports should be
31

designed to allow easy access to the vessel and fittings for inspection and
maintenance.
Though saddles are the most commonly used support for horizontal
cylindrical vessels, legs can be used for small vessels. A horizontal vessel will
normally be supported at two cross-sections. If more than two saddles are used the
distribution of the loading is uncertain. For a uniformly loaded beam the position will
be at 21 per cent of the span, in from each end. The saddle supports for a vessel
will usually be located nearer the ends than this value to make use of the stiffening
effect of the ends.
The saddles must be designed to withstand the load imposed by the weight
of the vessel and contents. They are constructed of bricks or concrete or are
fabricated from steel plate. The contact angle should not be less than 120
o
and will
not normally be greater than 150
o
. Wear plates are often welded to the shell wall to
reinforce the wall over the area of contact with the saddle. The dimensions of typical
standard saddle designs are given in figure below:

3.2.9 Type Of Flange And Selection
Flanged joints are used for connecting pipes and instruments to vessels, for
manhole covers and for removable vessel heads when ease of access is required.
Flanges may also be used on the vessel body when it is necessary to divide the
vessel into sections for transport or maintenance. Flanged joints are also used to
connect pipes to other equipment such as pumps and valves. Screwed joints are
often used for small-diameter pipe connections below 40 mm.
Several different types of flange are used for various applications. The
principal types used in the process industries are:
i. Welding-neck flanges
ii. Slip-on flanges, hub and plate types
iii. Lap-joint flanges
iv. Screwed flanges
v. Blank or blind, flanges
Welding-neck flanges (see Appendix A5 (a)) have a long tapered hub
between the flange ring and the welded joint. This gradual transition of the section
reduces the discontinuity stresses between the flange and branch, and increases
the strength of the flange assembly. Welding-neck flanges are suitable for extreme
service conditions where the flange is likely to be subjected to temperature, shear
and vibration loads. They will normally be specified for the connections and nozzles
on process vessels and process equipment.
Slip-on flanges (see Appendix A5 (b)) slip over the pipe or nozzle and are
welded externally and usually also internally. The end of the pipe is set back from 0
to 2.0 mm. The strength of a slip-on flange is from one-third to two-thirds that of the
corresponding standard welding-neck flange. Slip-on flanges are cheaper than
welding-neck flanges and are easier to align but have poor resistance to shock and
vibration loads. Slip-on flanges are generally used for pipe work.
Lap-joint flanges (see Appendix A5 (c)) are used for piped work and most
suitable in this design reactor. They are economical when used with expensive alloy
pipe such as stainless steel as the flange can be made from inexpensive carbon
steel. Usually a short lapped nozzle is welded to the pipe but with some schedules
of pipe the lap can be formed on the pipe itself and this will give a cheap method of
pipe assembly.
Screwed flanges (see Appendix A5 (d)) are used to connect screwed
fittings to flanges. They are also sometimes used for alloy pipe which is difficult to
weld satisfactorily. Blind flanges (blank flanges) are flat plates, used to blank off
33

flange connections, and as covers for manholes and inspection ports. So, in this
design lap joint flange is chosen as the best flange.

3.2.10 Gasket
Gaskets are used to make a leak-tight joint between two surfaces. It is
impractical to machine flanges to the degree of surface finish that would be required
to make a satisfactory seal under pressure without a gasket. The following factors
must be considered when selecting a gasket material:
i. The process conditions: pressure, temperature, corrosive nature of the
process fluid.
ii. Whether repeated assembly and disassembly of the joint is required.
iii. The type of flange and flange face

Up to pressures of 20 bar, the operating temperature and corrosiveness of the
process fluid will be the controlling factor in gasket selection. Vegetable fibre and
synthetic rubber gaskets can be used at temperatures of up to 100
o
C. Solid
polyfluorocarbon (Teflon) and compressed asbestos gaskets can be used to a
maximum temperature of about 260
o
C. Metal-reinforced gaskets can be used up to
around 450
o
C. Plain soft metal gaskets are normally used for higher temperatures.
So, compressed asbestos is chosen as the best gasket to be used in this reactor
design (see Appendix A6).

3.2.11 Flange Faces
Flanges are also classified according to the type of flange face used. There
are two basic types:
i. Full-faced flanges (see Appendix A7 (a)) where the face contact area
extends outside the circle of bolts; over the full face of the flange.
ii. Narrow-faced flanges (see Appendix A7 (b,c,d) where the face
contact area is located within the circle of bolts.
Full face, wide-faced, flanges are simple and inexpensive but are only
suitable for low pressures. The gasket area is large and an excessively high bolt
tension would be needed to achieve sufficient gasket pressure to maintain a good
seal at high operating pressures. The raised face, narrow-faced, flange shown in
34

Appendix A7 (b) is probably the most commonly used type of flange for process
equipment.
Where the flange has a plain face, as in Appendix A7 (b), the gasket is held
in place by friction between the gasket and flange surface. In the spigot and socket,
and tongue and grooved faces, Appendix A7 (c), the gasket is confined in a groove
which prevents failure by blow-out. Matched pairs of flanges are required, which
increases the cost, but this type is suitable for high pressure and high vacuum
service. Ring joint flanges, Appendix A7 (d), are used for high temperatures and
high pressure services. So, in this design raised face, narrow-faced is chosen as the
best flange faces.

3.2.11 CONCLUSION
In this work, the design of plug flow reactor has successfully been carried
out. From the calculation, the volume of the vessel is 189.3128 m
3
with 4.3151
diameter and 12.9453 length. The detail information of the design is as presented in
Table 1.2 and Table 1.3.

In designing a chemical plant, the mechanical design of the process equipments
such as pressure vessel, heat exchanger tube sheets, storage tanks, centrifuges
and etc are needed. The detailed mechanical designing of equipment is done by
mechanical engineers who are more familiar with the codes and design. On the
other hand, chemical engineer will be responsible in developing and specifying the
basic design information for particular equipment for specialist designer.
For falling-film evaporator, the data for mechanical design needed are:
i. Vessel function
ii. Process materials and services
iii. Operating and design temperature and pressure
iv. Materials of construction
v. Vessel dimensions and orientation
vi. Types of vessel heads to be used
vii. Openings and connections required
viii. Specification of internal fitting

3.3.1 Design Pressure
In designing a vessel, it needs to withstand the maximum pressure during
operation. For a vessel that is subjected to vacuum, the design should resist
the maximum differential pressure and is designed for full negative pressure
of 1 bar, unless it is fitted with an effective vacuum breaker.
The design pressure should be taken to be 10% above the normal
operating pressure:

3.3.2 Design Temperature
Since the strength of metals decreases with increasing temperature, the
maximum allowable design stress is evaluated at design temperature which
is the maximum working temperature of the material.
The design temperature can be evaluated with 5% safety factor above the
operating temperature:

36

3.3.3 Materials of Construction
Typically, the pressure vessel is made of plain carbon steel, low and high
alloy steels, alloys and etc. The material is selected based on its suitability
with the process environment and fabrication.
For the falling-film evaporator, the shell are filled with hot steam, thus,
constructed with stainless steel (SS304) while the tubes are constructed
from stainless steel (SS316) due to the mild corrosive of the feed which is
the ammonium nitrate solution of 72 wt%.

3.3.4 Design Stress
For the purpose of design, the value of maximum allowable stress that can
be accepted in the material of construction is needed. For the material to
able to withstand without failure under standard condition, a suitable design
stress factor (factor of safety) is applied to the maximum stress of the
material. This design stress factor is to cover any uncertainties in the design
methods, the loading, the quality of materials, and the workmanship. The
value can be taken from Appendix B.1 and typical design stress for material
can be taken from Appendix B.2.

3.3.5 Welded Joint Efficiency, and Construction Categories
The welded joint strength depends on the type of joint and the quality of the
welding. The allowable design stress of the material multiplied by a welded
joint factor will give the possible lower strength of a welded joint compared to
a virgin plate. Typical value of J is given in Appendix B.3. For the design of
this evaporator, J of 1.0 is taken because this value means that the joint is
equally strong as the virgin plate.

3.3.6 Corrosion Allowance
Corrosion allowance is the additional thickness of the metal to the design to
allow for corrosion and erosion, or scaling. The corrosion allowance for this
evaporator is 4mm because, the process material used in this equipment, i.e.
ammonium nitrate solution (75wt %-84wt %) may cause corrosion and
scaling to the equipment.

37

3.3.7 Design Loads
This equipment should be designed to resist loading at which a pressure
vessel will be subject during service. It can be divided into major and
subsidiary loads. Major load includes design pressure, maximum weight of
vessel and contents at operating temperature and hydraulic test condition,
wind loads, loads supported or reacting on the vessel. Subsidiary loads
includes local stresses caused by supports, internal structures and
connecting pipes; shock loads, bending moments, stresses due to difference
in temperature and loads caused by fluctuations in temperature and
pressure. Design load is further discussed in Section 2.4.

3.3.8 Minimum Practical Wall Thickness
The wall thickness should not be less than the value given below. (Include
corrosion allowance of 2mm)
Figure 2.1: Minimum practical wall thickness

3.3.9 Cylindrical Shells

The minimum thickness required to resist internal pressure is given by:

Where:

38

Process vessels that are operated under vacuum are subjected to external
pressure. The maximum pressure it will subject to is 1 bar (1 atm). In determining
the wall thickness required for process vessel subjected to external pressure, it is
required to know the failure through elastic instability (buckling).
The critical pressure to cause buckling, P
C
for long vessel with stiffening
ring is given by:

, value from Appendix B.4

3.3.10 Design of Stiffness Rings

Figure 2.2: Stiffness Ring
Load per unit length,

Second moment of area of the ring to avoid buckling,

Factor of safety taken as 6,

Critical load to cause buckling in a ring under uniform radial load,

:

39

3.3.11 Vessel Head

Vessel head are used as a closure of a cylindrical vessel.

Figure 2.1: Typical Head and Closure

3.3.11.1 Torispherical heads
For vessel subjected to internal pressure, the minimum thickness of
torispherical head is:

Where:

To avoid buckling, the ratio of knuckle to crown radii should not be
less than 0.06, and the crown radius should not be greater than the
diameter of the cylindrical section.
When it is subjected to external pressure,
Minimum vessel thickness,

(f)
(g)
(h)
40

For torispherical, radius R
s
is equivalent to Crown radius, R
c

3.3.11.2 Ellipsoidal heads
For vessel subjected to internal pressure, the minimum thickness of
ellipsoidal head is:

For typical design, the design constant and nominal diameter area as
follows:

From Figure 2.1,
i. (a) is flanged plate, for diameters less than 0.6m and corner radii
at least equal to 0.25e (Cp=0.45, De=Di);
ii. (b) and (c) is welded plate where the plate is welded to the end of
the shell with a fillet weld with angle of fillet of 45 and depth
equal to the plate thickness (Cp=0.55,De=Di)
iii. (d) is bolted cover with full gasket (Cp=0.4,De=bolt circle
diameter)
iv. (e) is bolted end-cover with a narrow-face gasket
(Cp=0.55,De=mean diameter of gasket)
41

The dead weight stress will be tensile (positive) for points below the
plane of vessel supports, and compressive (negative) for points above
the supports.
- Bending stress,

Where:

- Torsional shear stresses,
This stress is resulted from torque caused by loads offset from the vessel
axis. This load is usually small and need not be considered in preliminary
design.

Principal Stresses:

Where:
Total longitudinal stress,

If torsional shear stress, is negligible, principal stress will be

42

Compressive stress and elastic stability:
If the resultant axial stress,

due to the combined loading is compressive,
the failure of the vessel may be due to elastic instability (buckling). The
design must be check to make sure that the maximum value of the resultant
axial stress does not exceed the critical value at which buckling will occur.
Critical buckling stress,

iii. Wind Loads
For tall columns installed in the open, it is important to consider wind loading.
A wind speed of 160 km/h is usually taken for preliminary design which is
equivalent to 1280

wind pressure. The wind velocity is lower near the
ground than higher ground.

For a smooth cylindrical column or stack,
Dynamic wind pressure:

wind velocity, km/h

The loading per unit length of the column:

For a uniformly loaded cantilever the bending moment at any plane:

44

3.3.14 Skirt Supports

The skirt carried the load and is transmit to the foundation slab by the skirt
base ring (bearing plate). The moment produced by wind and other lateral
loads will tend to overturn the vessel. This will be opposed by the couple set
up by the weight of the vessel and the tensile load in the anchor bolts. Many
types of base ring designs as shown in Figure 2.1 is used with skirt support,
for example, rolled angle and plain flange rings suitable for small vessel and
double ring stiffened by gussets.

Figure 2.1: Flange ring design

Base Ring and Anchor Bolts:
The carried load by the skirt is transferred to the base ring or the foundation
slab (bearing plate). Winds and other loads produces moment that will tend
to overturn the vessel. The couple set up by the weight of the vessel and the
tensile load in the anchor bolt in turn, will oppose to the moment.
The following is the guide rules when selecting the anchor bolts given by
Scheiman:
- Bolts smaller than 25mm diameter should not be used
- Minimum number of bolts is 8
- Use multiple number of 4 bolts
- Bolt pitch should not be less than 600 mm

The maximum dead weight load on the skirt occurs when the vessel is full
with water.

Use data acquired previously,
46

- Total weight of skirt

- Wind loading,

Bending moment at base of skirt,

By trial and error,
Assume skirt thickness,
Previously,
Bending stress in the skirt,

Dead weight stress in the skirt,

At test condition, the vessel full of water for the hydraulic test,
,

At operating condition,

Maximum

Maximum

Take joint factor,
(Double-welded butt or equivalent type of joint and degree of radiography is
spot)
Criteria for design:
Maximum

Maximum

Both criteria are satisfied, add 4 mm for corrosion.

47

3.3.15 Piping and Flanges

Optimum diameter of flange:

Where:

Nozzle thickness:

Where:

3.3.16 Evaporator Tube-Plates

Tube-plates support the tubes, and separate the shell and tube side fluids.
Since, one side is subjected to shell-side pressure and tube-side pressure on
the other side. Therefore, the design must able to support the maximum
differential pressure that is likely to occur.
A tube plate is a perforated plate with an unperforated rim, supported at its
periphery. The holes of plate for the tubes weaken the plate and reduce its
flexural rigidity. In between the holes is a material that holds the holes
together is ligament. The presence of tubes strengthens the plate.

Ligament efficiency of perforated plate,

Where:

The plate must be thick enough to resist the bending and shear stresses
caused by the pressure load and any differential expansion of the shell and
tube.
48

The minimum plate thickness to resist bending can be estimated by:

Where:

The value of

is relies on the type of head,
Shear stress in the tube plate can be calculated by equating the pressure
force on the plate to the shear force in the material at the plate periphery.

Minimum plate thickness to resist shear is given by:

The design thickness is taken as the greater of the values obtained from
bending and shears resistance and must be greater than the minimum
thickness given from Appendix B.5

due to the combined loading is
compressive, the failure of the vessel may be due to elastic instability
(buckling). The design must be check to make sure that the maximum value
of the resultant axial stress does not exceed the critical value at which
buckling will occur.

Critical buckling
stress,

The maximum compressive stress will occur when the vessel is not under
pressure
=

is well below the critical buckling
stress.
So the design is satisfactory.

56

v. Vessel Support: Skirt Support
For tall vertical vessels, skirt supports are preferred because they do not
lead to concentrated local loads on the shell, it offers less restraint against
differential thermal expansion, and reduce the effect of discontinuity stresses
at the junction of the cylindrical shell and the bottom. The skirt support shall
be provided with at least one opening for inspection.

Carbon steel is chosen because this material mostly used in industry and
the prices is cheapest. Besides, it is routinely used for most organic chemicals and
neutral or basic aqueous solutions at moderate temperatures.

Joint efficiency was selected to be 1.0 because this implies that the joint is
equally as strong the virgin plate, complete weld length, and remaking any defects.
The lower joint factor will result in a thicker and heavier vessel.

Welded joint efficiency, 0 . 1 = J

3.5.5 Corrosion allowance

The corrosion allowance is the additional thickness of metal added to allow
for material lost by corrosion and erosion, or scaling. For carbon steel, where sever
corrosion is not expected, a minimum allowance of 2.0 mm should be used.

3.5.6 Minimum wall thickness

This is required to ensure that any vessel is sufficiently rigid to withstand its
own weight, and any incidental loads. As a general guide the wall thickness of any
vessel should not less than the values given below; this includes a corrosion
allowance of 2 mm.

Up to about 600
o
F (315
o
C), 85% magnesia has been the most popular
material. It is a mixture of magnesia and asbestos fibers so constructed that about
90% of the total volume is dead air space. Equivalents are available for situations
where asbestos is undesirable. Such insulants are applied to the equipment in the
form of slabs or blankets which are held in place with support and clips spotwelded
to the equipment. They are covered with cement to seal gaps and finished off with a
canvas that is trated for resistance to the weather. A galvanized metal outer cover
may be preferred because of its resistance to mechanical damage of the insulation.

Flanges joints are used for connecting pipes and instruments to vessel, for
manholes cover and for removable vessel head when ease of access is required.
Flanged may also be used on the vessel body, when it is necessary to divide the
vessel into sections for transport or maintenance. Flanges joint are also used to
connect pipe to equipments such as pumps and valves. Flanges range in size from
a few millimeters diameter for small pipes to several meters diameter for those used
as body or head flanges on vessels.

For the design of this heat exchanger, welding-neck flanges are used. It is
because welding-neck flanges have along tapered hub between the flange ring and
the welded joint. This gradual transition of the section reduces the discontinuity
stresses between the flange and branch and increases the strength of the flange
assembly. Welding-neck flanges and branch are suitable for extreme service
conditions, where flange are likely to be subjected to temperature, shear and
vibration loads. They will normally be specified for the connections and nozzles on
process equipment. The dimensions of welding-neck flanges is chosen base on the
nominal pipe size of the nozzle pipe. All dimensions are listed below.

Determination of support for a vessel will be depending on the design
temperature and pressure, vessel location and arrangement, and the internal
and external fittings. Support should be design to allow easy access to the
71

vessel for inspection and maintenance. Since heater is a horizontal
arrangement, saddle support is chosen as the support.

The saddle must be designed to withstand he load imposed by the weight of
the vessel and its contents. The design of saddle depends on the weight of
vessel, which is the weight of the heater itself. From previous calculation of
heater weight, the total weight is 18.4426 kN. From the value of weight, the
dimensions of saddle choose as referred to Figure 13.26 from Coulson &
Rochardson’s Volume 6. For outer shell diameter, D
shell
is 0.406m so 0.6m is
taken since it is the smallest value and the maximum weight is not exceeded.

Baffles are used in the shell to direct the fluid flow across tube and increase
the fluid velocity. When the fluid velocity increases, it is improving the rate of heat
transfer. The assembly of baffles and tubes are hold together by support rods and
spacers. The most commonly used type of baffle is the single-segmental baffle.
Baffle cut used to specify the dimensions of a segmental baffle. Generally, baffle cut
of 20%-25% will be optimum. The value will give good heat transfer rate without
excessive drop.
Type = single segmental
Baffle diameter = 0.406 m
Nb = length of tube / inside diameter shell
= 5000 / 406
= 12.3 ≈ 13 baffles

3.5.1 Operating and Design Temperature and Pressure
This column operates at temperature of 66.81°C and pressure of 1 atm.
The design pressure will be 10% above the operating pressure, to avoid spurious
operation during minor process upset. The design temperature at which the design
stress is evaluated is taken as the maximum operating temperature of the material,
with due allowance for any uncertainty involved in predicting vessel wall
temperatures.

3.5.2 Materials of Construction
As one of the process material involve is ammonium nitrate, the material of
construction of the column is required to be corrosion resistant. In this case stainless
steel type 304 is selected.

Table Typical design stresses for plate
(The appropriate material standards should be consulted for particular
grades and plate thicknesses)

Type of Head Minimum Thickness, e
Flat head 22mm
Ellipsoidal head 5mm
Torispherical head 5mm

By comparing the minimum thickness of these different type heads, it can
be concluded that either ellipsoidal or torispherical head are suitable to be choose
due to the economical factor since both require minimum thickness compared to flat
head.

3.5.5 The design of Column subject to Combined Loading

The main sources of load to be considered are dead weight loads and
wind. Meanwhile, the major sources of dead weight loads include vessel shell,
internal fittings (packed bed) and external fittings (ladders, platforms, piping).

Wind loading will only be important on tall columns installed in the open.
Columns are usually free standing, mounted on skirt support and not attached to
structural steel work. Under this conditions, the vessel under wind loading acts as
cantilever beam.
Take wind speed, U
w
= 160 km/h
To estimate the wind pressure, the following equation is used:
P
w
= 0.05 U
w
2

hence, large wall thicknesses), cladding is normally recommended in order to reduce the vessel cost when alloy steels are used. Reactor construction material used is stainless steel 16Cr-2Mo-8Ni (316). By referring to the standard code The American Society of Mechanical Engineers (ASME), the maximum stress is 133.5 N/mm2.

THE EFFICIENCY OF WELDED JOINT There are several methods to make welded joints. In particular case the

choices of a type from the numerous alternatives depend on: 1. The circumstances of welding. In many cases the accessibility of the joint determines the types of welding. In a small diameter vessel (under 18-24 inches) from the inside, no manual welding can be applied. Using backing strip it must remain in place. In larger diameter vessels if a manway is not used, the last (closing) joint can be welded from outside only. The type of welding may be determined also by the equipment of the manufacturer. 2. The requirements of the code. Regarding the type of joint the Code establishes requirements based on service, material and location of the welding. The welding processes that may be used in the construction of vessels are also restricted by the Code as described in paragraphUW-27. 3. The aspect economy. If the two preceding factors allow free choice, then the aspect of economy must be the deciding factor. Some considerations concerning the economy of welding’s: 1. V-edge preparation, which can be made by torch cutting, is always more econornical than the use of J or U preparation. 2. Double V preparation requires only half the deposited weld metal required for single V preparation. 3. Increasing the size of fillet weld, its strength increases in direct proportion, while the deposited weld metal increases with the square of its size. 4. Lower quality welding makes necessary the use of thicker plate for the vessel. Whether using stronger welding and thinner plate or the opposite is more economical, depends on the size of vessel, welding equipment, etc. This must be decided in each particular case The strength of a welded joint depends on the type and quality of welding joint. Then, for design purposes weld joint efficiency, J = 1.0 was chosen. This selection is based on ASME UW-2 stated that:

3

“… all butt welded joints shall be fully radiographe, except under provision OS UW-2(a)(2) and UW-2(a)(3) below and UW-4(a)(4)….” This statement is clarifying the requirement of welded joint that fully radiograph when pressure vessel containing lethal substances. So, all main category A and B welds must be fully radiographed. But category B and C welds in a nozzle and communicating chambers that are not larger than 10 inch nominal pipe size and do not exceed 1to 1/8 inch thick are exempt. Based on the fluid composition contain in the reactor for this design, ammonium nitrate could be a dangerous and lethal substance if leaking to the atmosphere. Furthermore, ammonia also potentially dangerous substance. The location of A, B and C shown in Figure 5.3.

The pressure given in the table only design stress for selected material but for design stress pressure that generated by the fluid also need to take into consideration. From book of Pressure Vessel Handbook 10th edition page 29 giving

4

Specific gravity for the fluid in the reactor is 0.385SE
where P = Design pressure. P Inside diameter.0
DO t 0
= 15 m = 0.4.4 m = 133.
3. N/mm2 5
. L Design pressure.5 N/mm2
Determination of reactor thickness.2
Design temperature Operating temperature = 185 0C Take 10 percent above operating temperature.80 m = 2.4.1. the value needs to multiply with specific gravity of fluid or other calculation is:
Value above is for the water.the pressure of water that will emit at different length. R Allowable stress. J = 1. But for other material.1.778 N/mm2 = 4.3
Thickness of cylindrical vessel Data required to performed calculation Cylinder length.
So design pressure should be taken is:
Taking 10 per cent above as design pressure
3. S Joint efficiency. To get the pressure in the reactor emit by the fluid is multiply value get by specific gravity of fluid.1067. assume i)
for cylinder wall
Tangential stress with condition t < R/2 and P< 0. Di Inside radius of reactor.

7
.0 mm. N/mm2 = Joint efficiency
Use bolted cover with a full face gasket Cp = 0. 4. Take as same thickness allowance of 4 mm as wall 18. take as approx. m = Stress value of material. N/mm2 = Inside diameter.
Flat head
Where P De f Cp = Design pressure.
(ii)
Try a “standard” ellipsoidal head.
So an ellipsoidal head would probably be the most economical. ellipsoidal head will be used as domed head for reactor. m = Stress value of material.4 De= bolt circle diameter. from equation 5. N/mm2 = Joint efficiency
Therefore. ratio major : minor axes = 2 : 1
Where P D f J = Design pressure.46
This shows the inefficiency of a flat cover.80 m. N/mm2 = Bolt diameter. It would be better to use a flanged domed head.= Stress concentration factor for torispherical heads Therefore. Therefore. So.

and this should be allowed for when calculating the area available for heat transfer. N/mm2 = Elastic modulus of shell.5
Tube sheet (plate) Tube sheet forms the barrier between shell and tube fluids. from equation 5. The thickness of tube sheet will reduce the effective length of the tube slightly. mm = Outlet diameter of tube.49
Substituted k value into equation 5. N/mm2 = Elastic modulus of tube.4. N/mm2 Therefore. and where it is
essential for safety or process reason to prevent any possibility of intermixing due to leakage at the tube sheet joint.1.3. N/mm2 = Design stress. mm = Design pressure. double tube-sheets can be used.47 8
. with the space between the sheet vented.48
Substituted F value inside equation 5. mm = Number of tube = Thickness of tube. mm = Thickness of shell. The thickness of tube sheet calculation given by the TEMA standard as below Thickness of tube sheet
Where
and
Where = Outlet diameter of shell.

kg 9
. such as plates.6565 kg Therefore for 15m length = 81. 1 foot of pipe has weight 3.2
Weight of tubes
Density of stainless steel 316 = 7787 kg/m3 (Obtain from Incropera De Witt.15 for distillation columns. and with plate support rings.47
3. which can be taken as = 1.6.1. Hv g t pm Dm = height. from equation 5.0 mm = density of vessel material = 7787 kg/m3.
Cv taken is 1.19) 0. N.4. between tangent lines (the length of the cylindrical section) = 15 m = gravitational acceleration. Heat and Mass Transfer) From Pressure Vessel Handbook 10th Edition For 2-in tube. or length. = a factor to account for the weight of nozzles.4. Therefore. or similar vessels.6 3.652 lbm=1.3048 m = 1 ft 3. = wall thickness = 18. internal supports.81 m/s2. 9. excluding internal fittings.6. with several man ways.5207 kg
Where = Mass of single tubes.4.652 lb (Properties are based on ANSI B36.1. = 1. etc.08 for a few internal fittings.08 for vessels with only a few internal fittings.3.1
Reactor load Weight of a cylindrical vessel with domed end
Where Wv Cv = total weight of the shell.818 m. or equivalent fittings. man ways. = mean diameter of vessel D =4.1.

The
former is supported by two saddles can be considered as a simple supported beam with uniformly distributed load.7. from equation 5.57
3.4.1. The distribution of the longitudinal axis of the bending moment is shown in the diagram below:
12
. m = Thickness of shell. mm Therefore.58
3. kN = Inside diameter. N/mm2 = Inside diameter. from equation 5.8
Support Support saddle used to support the container in a horizontal reactor. mm = Thickness of shell.2
Direct stress Direct stress is the stress that generated by the fluid inside vessel and its
vessel weight
Where = Total weight of reactor (shell).ii)
Longitudinal stress
Where = Design stress. m Therefore.4.1.

In theory.218 m Q = Total weight/saddle. giving rise to the maximum bending moment is the lowest position when the magnitude of the maximum value on both sides is equal to the value of support in the middle of the range of:
M L1  2M L 2
Where A L H = Distance from the tangent to the saddle support.The maximum point occurs on both sides and support the middle range. the optimum support position. the tangent line. m
Bending moments at the two saddle supports. N = Total weight/2 = 1144. can be determined using the following equations:
13
.4 m b = width of saddle. m = column depth.6171 kN R = Radius of reactor = 2. and bending in the middle of the range. m = 1. m = Length of the container.

bending moment is classified as the stress generated as a resultant to the dead weight of reactor in horizontal position supported by the saddle support. value for A =3. Bending stress longitudinal to the cross sectional area of shell as
Where
M L1
Ih
D t
= = = =
Longitudinal bending stress at mid-span Second moment of area of the shell Shell diameter Shell thickness
Therefore.4.97m Therefore
3.Balance from the bending moment:
Solving from above equation.9
Stresses in vessel wall Bending stress is a stress that cause by the bending moment in the shell
(vessel).1.
Resultant axial stress due to bending and pressure is given by:
Where = Longitudinal bending moment at the support = an empirical constant: 1
14
.


Upwind stress
Therefore. This stress is given as follows:
Where = Longitudinal bending moment at the support = an empirical constant: 1.
Because of the stress difference is <the maximum stress. S.
Principal stress.
Downwind stress
Therefore.0 for stiffened shell. 2 is smaller than the maximum design stress allowable S. this means that some of the top cross section is not effective against longitudinal bending. If the shell does not remain round when loaded.
Because the value of b. then the pressure vessel design of the heat exchanger is acceptable. The magnitude of the longitudinal bending stress on the strengthening of support will depend on the local shell. Therefore.
The difference in principal stresses and the longitudinal stress resultant.
Longitudinal stress. 15
. the design is acceptable.

150
0 6 2
1 7
1
2 3
3
16
.1.
Table 5.80 .99
6 .10
Saddle design Saddle must be designed to withstand heavy loads caused by the container
and its contents.8 m is used after interpolation been made as shown in Table 5.86 m.303
4 . the contact angle cannot be less than 120° and not more than 1500. Smooth plates (wear plate) are usually welded to the shell wall to reinforce the wall area in contact with the saddle. the former equal to the diameter of 4.3. This saddle is made of stainless steel plate.3. Typically. standard steel saddles to container with a diameter of 4. Saddle support design procedure given by Brownell and Young (1959) and Megyesy (1977).4.07
3 .525
0 .852
1 .3 Standard steel saddle V essel Diameter (m) V Y C E J
2G 1
Dimension (m)
mm B tolt t olt B
diameter hole
4 .

hub and plate types. or blind. namely: 1. less than 40 mm. Flange connections are also used to attach sections of pipe on the installation and opening of facilities needed for maintenance. Blank. and vibration. 3.11
Design bolt flange connection Flange can be used in the body of the container when the container must
be divided into several sections for easy removal and maintenance. the flange of this type is selected for its ability to withstand extreme operating conditions likely to be exposed to temperature loading. but the structure of the pipe is usually welded to reduce costs. There are four openings in the design of the reactor tube and shell. from a few millimeters in diameter for small pipes to several meters in diameter for use as a body or head flange on the container. Screwed flanges. flanges. Flange sizes vary. 2. 4.4.5 bar (650 kPa) at a temperature of 155 C design. Lap-joint flanges. Given the pressure vessel is operated under the operating pressure of 6. Optimum size for the flange to the nozzles feed (input) and the output of the shell and tube can be determined using the following equation proposed by Sinnot:
17
. shear. Welding-neck flanges. which requires the use of connection. Flange connection used to connect pipes to other equipment such as pumps and valves. Slip-on flanges. Typically used for connecting the connection of bolt with small diameter pipes.
Welded-neck flange type (steel) used for opening the input and output openings for the connection and the nozzle of the reactor tube and shell.1.3. 5.

This will normally be 5 to 10 per cent above the normal working pressure.3.36)
3.37)
0
C K
3. (1.2
Design Temperature The operating temperature of our reactor is taken as 185 0C. the design pressure of this reactor is taken as 10% above the operating temperature to avoid spurious operation during minor process upsets. The material selected must have sufficient strength and be easily worked. In this design. to avoid spurious operation during minor process upsets. To impart corrosion resistance the chromium content must be above 12 per cent and the higher the chromium content. R2
3. For vessels under internal pressure. Stainless steels are the most frequently used corrosion resistant materials in the chemical industry. The most economical material that satisfies both process and mechanical requirements should be selected which is this will be the material that gives the lowest cost over the working life of the plant and allowing for maintenance and replacement.2.2.2
REACTOR 2. Nickel is added to improve the corrosion resistance in non-oxidising environments. the design pressure is normally taken as the pressure at which the relief device is set. For safety
reason. the more resistant is the alloy to corrosion in oxidising conditions. 24
.3
Material Of Construction Many factors have to be considered when selecting engineering materials
but for chemical process plant the overriding consideration is usually the ability to resist corrosion. considering 10 % safety factor so that the design pressure become as below: (1.1
Design Pressure A vessel must be designed to withstand the maximum pressure to which it
is likely to be subjected in operation.2.

38) Where:
.
25
. It contains the minimum Cr and Ni that give a stable austenitic structure. as conclusion stainless steels type 304 is the best material of construction and then selected as material of construction for the reactor. the inside diameter f. the design pressure Di . minimum thickness
Pi .2.
3. Sinnot. Type 304 also-called 18/8 stainless steels is the most generally used stainless steel. Chemical Engineering Design). The uniform structure of austenitic is the structure desired for corrosion resistance and it is these grades that are widely used in the chemical industry. so the maximum allowable design stress will depend on the material temperature. is f = 115 N/mm2 = 115 bar (R.A wide range of stainless steels is available. The carbon content is low enough for heat treatment not to be normally needed with thin sections to prevent weld decay. with compositions tailored to give the properties required for specific applications. With design temperature is equal to maximum operating temperature.4
Determination Of Minimum Thickness Of The Reactor (1.K. 1999. The design temperature at which the design stress is evaluated should be taken as the maximum working temperature of the material. Typical design stress values for some common materials are shown in Appendix A2.38). design stress
The strength of metals decreases with increasing temperature. particularly at elevated temperatures (see Appendix A1). Thus from Eqn. The austenitic stainless steels have greater strength than the plain carbon steels. design stress for stainless steel 304. 185 oC. (1. So.

Corrosion is a complex phenomenon and it is not possible to give specific rules for the estimation of the corrosion allowance required for all circumstances. where severe corrosion is not expected. joint factor =1 f. crown radius = Di
26
. Standard torispherical heads (dished ends) are the most commonly used end closure for vessels up to operating pressures of 15 bar.002 m =
3. iv. (1. iii. or scaling. Flat heads Hemispherical heads Ellipsoidal heads Torispherical heads
The heads used for the vessel may be flat if they are suitably buttressed but preferably they are some curved shape as the hemispherical.2. For carbon and low-alloy steels. ellipsoidal or torispherical heads. They can be used for higher pressures.
Add allowance for corrosion =
+ 0.5
Design of Vessel Heads The end of a cylindrical vessel is closed by heads of various shapes. The minimum thickness of torispherical and ellipsoidal head can be calculated by using equation below: For torispherical heads. design stress Rc. Above 15 bar an ellipsoidal head will usually prove to be the most economical closure to use. The
common types used are: i. ii.39)
Where Pi .The corrosion allowance is the additional thickness of metal added to allow for material lost by corrosion and erosion.0 mm should be used. internal pressure J . a minimum allowance of 2. The allowance should be based on experience with the material of construction under similar service conditions to those for the proposed design. but above 10 bar their cost should be compared with that of an equivalent ellipsoidal head.

the design temperature and pressure.1737) m = 4.44)
Where. Supports will impose localized loads on the vessel wall and the design must be checked to ensure that the resulting stress concentrations are below the maximum allowable design stress.
3. The vessel will be filled with water for the hydraulic pressure test and may fill with process liquid due to misoperation. Cv = a factor account for the weight of nozzles. the vessel location and arrangement and the internal and external fittings and attachments.2. man ways = 1.
External fittings: ladders. v.08 for vessel with only a few internal fittings = 1.3151 m + 2(0.iv.
For preliminary calculations the approximate weight of a cylindrical vessel with domed ends and uniform wall thickness. shape and
weight of the vessel.6625 m
Hv = height/length of the cylindrical area = 12. piping. The weight of liquid to fill the vessel. platforms. can be estimated from the following equation: (1. and any superimposed loads. Supports should be 30
. The supports must be designed to carry the weight of the vessel and contents. Horizontal vessels are usually mounted on two saddle supports (see Appendix A4).8
Vessel Support The method used to support a vessel will depend on the size.15 for vessel with several man ways and other fittings
Dm = mean diameter of the vessel = Dm + t = 4. such as wind loads.9453 m
Thus.

They are constructed of bricks or concrete or are fabricated from steel plate. Heinemann). The saddles must be designed to withstand the load imposed by the weight of the vessel and contents.K. Though saddles are the most commonly used support for horizontal cylindrical vessels. legs can be used for small vessels. If more than two saddles are used the distribution of the loading is uncertain. The contact angle should not be less than 120o and will not normally be greater than 150o. Oxford.4: The Dimensions of Typical Standard Saddle Designs (Source: Sinnott. 31
Butterworth-
. For a uniformly loaded beam the position will be at 21 per cent of the span. Wear plates are often welded to the shell wall to reinforce the wall over the area of contact with the saddle. Coulson & Richardson’s Chemical Engineering. Vol. R.designed to allow easy access to the vessel and fittings for inspection and maintenance. A horizontal vessel will normally be supported at two cross-sections. 6: “Chemical Engineering Design”. The dimensions of typical standard saddle designs are given in figure below:
Figure 1. The saddle supports for a vessel will usually be located nearer the ends than this value to make use of the stiffening effect of the ends. 1999. in from each end.

and increases the strength of the flange assembly. shear and vibration loads. This gradual transition of the section reduces the discontinuity stresses between the flange and branch. iii. The strength of a slip-on flange is from one-third to two-thirds that of the corresponding standard welding-neck flange. flanges
Welding-neck flanges (see Appendix A5 (a)) have a long tapered hub between the flange ring and the welded joint. Screwed flanges (see Appendix A5 (d)) are used to connect screwed fittings to flanges.9
Type Of Flange And Selection Flanged joints are used for connecting pipes and instruments to vessels. iv. Several different types of flange are used for various applications. Usually a short lapped nozzle is welded to the pipe but with some schedules of pipe the lap can be formed on the pipe itself and this will give a cheap method of pipe assembly. hub and plate types Lap-joint flanges Screwed flanges Blank or blind. Slip-on flanges are generally used for pipe work. Slip-on flanges (see Appendix A5 (b)) slip over the pipe or nozzle and are welded externally and usually also internally. v.0 mm. The principal types used in the process industries are: i. for
manhole covers and for removable vessel heads when ease of access is required. ii. Lap-joint flanges (see Appendix A5 (c)) are used for piped work and most suitable in this design reactor. Flanged joints are also used to connect pipes to other equipment such as pumps and valves.2. They will normally be specified for the connections and nozzles on process vessels and process equipment.3. They are economical when used with expensive alloy pipe such as stainless steel as the flange can be made from inexpensive carbon steel. The end of the pipe is set back from 0 to 2. used to blank off 32
. Slip-on flanges are cheaper than welding-neck flanges and are easier to align but have poor resistance to shock and vibration loads. Blind flanges (blank flanges) are flat plates. Welding-neck flanges Slip-on flanges. Flanges may also be used on the vessel body when it is necessary to divide the vessel into sections for transport or maintenance. They are also sometimes used for alloy pipe which is difficult to weld satisfactorily. Welding-neck flanges are suitable for extreme service conditions where the flange is likely to be subjected to temperature. Screwed joints are often used for small-diameter pipe connections below 40 mm.

Vegetable fibre and synthetic rubber gaskets can be used at temperatures of up to 100 oC. Metal-reinforced gaskets can be used up to around 450 oC. So.2. ii. ii. wide-faced. temperature. The process conditions: pressure.d) where the face contact area is located within the circle of bolts.11
Flange Faces Flanges are also classified according to the type of flange face used. Solid polyfluorocarbon (Teflon) and compressed asbestos gaskets can be used to a maximum temperature of about 260 oC. Narrow-faced flanges (see Appendix A7 (b. The type of flange and flange face Up to pressures of 20 bar. The gasket area is large and an excessively high bolt tension would be needed to achieve sufficient gasket pressure to maintain a good seal at high operating pressures.10 Gasket Gaskets are used to make a leak-tight joint between two surfaces. So. Whether repeated assembly and disassembly of the joint is required.2. The following factors must be considered when selecting a gasket material: i. in this design lap joint flange is chosen as the best flange.c. narrow-faced. Full face. 3. compressed asbestos is chosen as the best gasket to be used in this reactor design (see Appendix A6). corrosive nature of the process fluid. the operating temperature and corrosiveness of the process fluid will be the controlling factor in gasket selection. and as covers for manholes and inspection ports. Full-faced flanges (see Appendix A7 (a)) where the face contact area extends outside the circle of bolts. flange shown in
33
. Plain soft metal gaskets are normally used for higher temperatures.
iii. The raised face. flanges are simple and inexpensive but are only suitable for low pressures. It is impractical to machine flanges to the degree of surface finish that would be required to make a satisfactory seal under pressure without a gasket. over the full face of the flange. There
are two basic types: i.flange connections.
3.

but this type is suitable for high pressure and high vacuum service. Where the flange has a plain face. In the spigot and socket. the gasket is confined in a groove which prevents failure by blow-out. From the calculation.2 and Table 1.
Table 1. Ring joint flanges. Appendix A7 (c). Matched pairs of flanges are required.3151 diameter and 12. N Vessel support Type of flanges Gasket Flange Faces 8. bar Operating temperature.11
CONCLUSION In this work. and tongue and grooved faces. as in Appendix A7 (b). Appendix A7 (d).2. narrow-faced is chosen as the best flange faces. the volume of the vessel is 189.3128 m3 with 4.1737 Torispherical 3500 Saddle support Lap-joint flange Compressed asbestos Raised face. are used for high temperatures and high pressure services. The detail information of the design is as presented in Table 1.3: Summary of mechanical design Operating pressure.9453 length. in this design raised face.Appendix A7 (b) is probably the most commonly used type of flange for process equipment.65 0. m Type of head Total weight of reactor. the design of plug flow reactor has successfully been carried
out.3. k Thickness of reactor. the gasket is held in place by friction between the gasket and flange surface.
3.8 476. which increases the cost. So. narrow-faced
34
.

The design pressure should be taken to be 10% above the normal operating pressure:
3. ii. the maximum allowable design stress is evaluated at design temperature which is the maximum working temperature of the material. For a vessel that is subjected to vacuum. the mechanical design of the process equipments such as pressure vessel. vi.1
Design Pressure In designing a vessel. v. chemical engineer will be responsible in developing and specifying the basic design information for particular equipment for specialist designer. vii. unless it is fitted with an effective vacuum breaker. the design should resist the maximum differential pressure and is designed for full negative pressure of 1 bar. On the other hand. it needs to withstand the maximum pressure during operation.3.3
FALLING FILM EVAPORATOR 1. the data for mechanical design needed are: i.3. viii.3. Vessel function Process materials and services Operating and design temperature and pressure Materials of construction Vessel dimensions and orientation Types of vessel heads to be used Openings and connections required Specification of internal fitting
3. storage tanks. iii. F1
In designing a chemical plant. The detailed mechanical designing of equipment is done by mechanical engineers who are more familiar with the codes and design. For falling-film evaporator. iv. The design temperature can be evaluated with 5% safety factor above the operating temperature:
35
. heat exchanger tube sheets. centrifuges and etc are needed.2
Design Temperature Since the strength of metals decreases with increasing temperature.

alloys and etc.e.
3. The material is selected based on its suitability with the process environment and fabrication. J of 1.5
Welded Joint Efficiency.3. thus.6
Corrosion Allowance Corrosion allowance is the additional thickness of the metal to the design to allow for corrosion and erosion.3
Materials of Construction Typically. the shell are filled with hot steam. the quality of materials. The corrosion allowance for this evaporator is 4mm because.3.
3.3. ammonium nitrate solution (75wt %-84wt %) may cause corrosion and scaling to the equipment. and the workmanship. low and high alloy steels. the pressure vessel is made of plain carbon steel. the process material used in this equipment. constructed with stainless steel (SS304) while the tubes are constructed from stainless steel (SS316) due to the mild corrosive of the feed which is the ammonium nitrate solution of 72 wt%. The value can be taken from Appendix B. This design stress factor is to cover any uncertainties in the design methods.0 is taken because this value means that the joint is equally strong as the virgin plate. For the design of this evaporator. the value of maximum allowable stress that can be accepted in the material of construction is needed. The allowable design stress of the material multiplied by a welded joint factor will give the possible lower strength of a welded joint compared to a virgin plate. and Construction Categories The welded joint strength depends on the type of joint and the quality of the welding. Typical value of J is given in Appendix B.
36
.4
Design Stress For the purpose of design.3. the loading.2.3.3.1 and typical design stress for material can be taken from Appendix B. i. For the material to able to withstand without failure under standard condition. a suitable design stress factor (factor of safety) is applied to the maximum stress of the material.
3. or scaling. For the falling-film evaporator.

It can be divided into major and subsidiary loads. bending moments. internal structures and connecting pipes. Major load includes design pressure. stresses due to difference in temperature and loads caused by fluctuations in temperature and pressure.
3. wind loads.3. (Include corrosion allowance of 2mm) Figure 2.7
Design Loads This equipment should be designed to resist loading at which a pressure vessel will be subject during service.3. Subsidiary loads includes local stresses caused by supports. loads supported or reacting on the vessel.4. maximum weight of vessel and contents at operating temperature and hydraulic test condition.8
Minimum Practical Wall Thickness The wall thickness should not be less than the value given below.9
Cylindrical Shells
The minimum thickness required to resist internal pressure is given by:
Where:
37
. Design load is further discussed in Section 2.1: Minimum practical wall thickness
3.3. shock loads.3.

it is required to know the failure through elastic instability (buckling). The maximum pressure it will subject to is 1 bar (1 atm). The critical pressure to cause buckling. value from Appendix B.10 Design of Stiffness Rings
Figure 2. In determining the wall thickness required for process vessel subjected to external pressure.2: Stiffness Ring Load per unit length.
Factor of safety taken as 6. :
38
. Second moment of area of the ring to avoid buckling. PC for long vessel with stiffening ring is given by:
.Process vessels that are operated under vacuum are subjected to external pressure. Critical load to cause buckling in a ring under uniform radial load.3.4
3.

When it is subjected to external pressure.3.
39
.1 Torispherical heads For vessel subjected to internal pressure.11.1: Typical Head and Closure
3. the ratio of knuckle to crown radii should not be less than 0.3.11 Vessel Head
Vessel head are used as a closure of a cylindrical vessel.06.
(f)
(g)
(h) Figure 2. the minimum thickness of torispherical head is:
Where:
To avoid buckling.3. Minimum vessel thickness. and the crown radius should not be greater than the diameter of the cylindrical section.

for diameters less than 0.45.De=Di) iii. i. (e) is bolted end-cover with a narrow-face gasket
(Cp=0. Minimum vessel thickness.2 Ellipsoidal heads For vessel subjected to internal pressure.55. h = height of the head from the tangent line. (a) is flanged plate.25e (Cp=0. 2b = minor axis = 2h.3. For ellipsoidal. .11. Rc 3.1.11. (b) and (c) is welded plate where the plate is welded to the end of the shell with a fillet weld with angle of fillet of 45 and depth equal to the plate thickness (Cp=0. De=Di). (d) is bolted cover with full gasket (Cp=0.55. ii.3 Flat ends Minimum thickness of flat end required for internal pressure:
Where:
For typical design.De=bolt circle diameter) iv.
3. the design constant and nominal diameter area as follows:
From Figure 2. radius Rs is equivalent to Crown radius.De=mean diameter of gasket) 40
.3.
Where 2a = major axis = Do. the minimum thickness of ellipsoidal head is:
When subjected to external pressure.4.For torispherical.6m and corner radii at least equal to 0.

3.  Bending stress.
Where:

Torsional shear stresses. If torsional shear stress.3. is negligible. principal stress will be
41
.12 Stresses Analysis Primary Stresses:  Longitudinal and circumferential stresses due to internal or external pressure:

Direct stress weight.
Principal Stresses:
Where: Total longitudinal stress. This stress is resulted from torque caused by loads offset from the vessel axis. and compressive (negative) for points above the supports.
The dead weight stress will be tensile (positive) for points below the plane of vessel supports. This load is usually small and need not be considered in preliminary design.

13 Weight Loads The weight loads comprises of: i. steel including typical liquid loading. and uniform wall thickness. Vessel Shell
The approximate weight of a cylindrical vessel with domed ends.
the failure of the vessel may be due to elastic instability (buckling). The design must be check to make sure that the maximum value of the resultant axial stress does not exceed the critical value at which buckling will occur. 1. the following can be used: (a) Caged ladders.7
(d) Contacting plates.2 area
42
.3. steel. 360 (b) Plain ladders. 1. due to the combined loading is compressive. Critical buckling stress. for vertical columns. Weight of Vessel:
Where:
ii.
3. 150 length length area plate
(c) Platforms.Compressive stress and elastic stability: If the resultant axial stress. steel. steel.
Vessel Fittings For vessel fittings.

A wind speed of 160 km/h is usually taken for preliminary design which is equivalent to 1280 wind pressure.
Wind Loads
For tall columns installed in the open.e. i.For Internal Fittings. The wind velocity is lower near the
ground than higher ground. Dynamic wind pressure:
wind velocity.
For a smooth cylindrical column or stack. tubes: Weight of Tubes:
Where:
iii. it is important to consider wind loading. km/h
The loading per unit length of the column:
For a uniformly loaded cantilever the bending moment at any plane:
43
.

will oppose to the moment. This will be opposed by the couple set up by the weight of the vessel and the tensile load in the anchor bolts. Winds and other loads produces moment that will tend to overturn the vessel.1 is used with skirt support. The following is the guide rules when selecting the anchor bolts given by Scheiman:     Bolts smaller than 25mm diameter should not be used Minimum number of bolts is 8 Use multiple number of 4 bolts Bolt pitch should not be less than 600 mm
Approximate pitch circle diameter Circumference of bolt circle Minimum recommended bolt spacing Number of bolts required. for example. Many types of base ring designs as shown in Figure 2.
Figure 2. rolled angle and plain flange rings suitable for small vessel and double ring stiffened by gussets.1: Flange ring design
Base Ring and Anchor Bolts: The carried load by the skirt is transferred to the base ring or the foundation slab (bearing plate). The moment produced by wind and other lateral loads will tend to overturn the vessel.3. The couple set up by the weight of the vessel and the tensile load in the anchor bolt in turn. at minimum recommended bolt spacing
44
.14 Skirt Supports
The skirt carried the load and is transmit to the foundation slab by the skirt base ring (bearing plate).3.

Previously.
Maximum Maximum Take joint factor. At test condition.
46
. (Double-welded butt or equivalent type of joint and degree of radiography is spot) Criteria for design: Maximum Maximum
Both criteria are satisfied.
At operating condition. 
Total weight of skirt Wind loading.
Bending moment at base of skirt. Bending stress in the skirt. the vessel full of water for the hydraulic test. Dead weight stress in the skirt. . Assume skirt thickness. add 4 mm for corrosion.
By trial and error.

15 Piping and Flanges
Optimum diameter of flange:
Where:
Nozzle thickness:
Where:
3. Where:
The plate must be thick enough to resist the bending and shear stresses caused by the pressure load and any differential expansion of the shell and tube. Therefore. supported at its periphery.3.3. A tube plate is a perforated plate with an unperforated rim.16 Evaporator Tube-Plates
Tube-plates support the tubes. The presence of tubes strengthens the plate. 47
. the design must able to support the maximum differential pressure that is likely to occur. In between the holes is a material that holds the holes together is ligament. and separate the shell and tube side fluids.
Ligament efficiency of perforated plate.3. The holes of plate for the tubes weaken the plate and reduce its flexural rigidity. one side is subjected to shell-side pressure and tube-side pressure on the other side. Since.

The minimum plate thickness to resist bending can be estimated by:
Where:
The value of
is relies on the type of head.
Minimum plate thickness to resist shear is given by:
The design thickness is taken as the greater of the values obtained from bending and shears resistance and must be greater than the minimum thickness given from Appendix B.5
48
.
Shear stress in the tube plate can be calculated by equating the pressure force on the plate to the shear force in the material at the plate periphery.

Second moment of area of the ring to avoid buckling. Load per unit length.
51
.Design of Stiffness Ring:
Assume.
:
Since.
Vessel heads: If using torispherical head.  Subjected to internal pressure
Where:
Plus corrosion allowance of 4mm.
Taken factor of safety = 6.
Critical load to cause buckling in a ring under uniform radial load. The length and diameter of stiffening ring are acceptable.

iv. the resultant axial stress.5 . The design must be check to make sure that the maximum value of the resultant axial stress does not exceed the critical value at which buckling will occur. the failure of the vessel may be due to elastic instability (buckling). .
The radial stress is negligible.7193 6. So the design is satisfactory. is well below the critical buckling
55
.
Critical stress.3349
7.
12.3349
Up-wind
Down-wind
The greatest difference between the principal stresses will be on the downwind side.5768
7. where it is well below the maximum allowable design stress of 125.Since the torsional shear stress is negligible.
buckling
The maximum compressive stress will occur when the vessel is not under pressure = stress. due to the combined loading is
compressive. the principle stress will be and .
Elastic Stability (Buckling) Previously.

Total weight of skirt . f at ambient temperature = Young’s Modulus at ambient temperature.
Previously. Material of Construction = Plain Carbon Steel Design stress. Height of Skirt. 56
. Weight of vessel. At test condition.
Dead weight stress in the skirt. Bending stress in the skirt.
Wind loading.v. Bending moment at base of skirt. .
Vessel Support: Skirt Support For tall vertical vessels. and reduce the effect of discontinuity stresses at the junction of the cylindrical shell and the bottom. Take skirt thickness.
By trial and error.
Skirt thickness: Try straight cylindrical skirt. Previously. the vessel full of water for the hydraulic test.
The maximum dead weight load on the skirt occurs when the vessel is full with water. The skirt support shall be provided with at least one opening for inspection. it offers less restraint against differential thermal expansion. skirt supports are preferred because they do not lead to concentrated local loads on the shell.

The design thickness is taken as the greater of the values obtained from bending and shears resistance and must be greater than the minimum thickness given from Appendix B.
Opening and Nozzles:
Optimum diameter of flange:
Nozzle thickness:
Feed Inlet:
Concentrate Outlet:
Vapor Outlet:
Steam Inlet:
59
.5
viii.

5
Corrosion allowance
The corrosion allowance is the additional thickness of metal added to allow for material lost by corrosion and erosion. where sever corrosion is not expected.3. complete weld length. Besides.5.5. and remaking any defects. As a general guide the wall thickness of any vessel should not less than the values given below.5. J  1. this includes a corrosion allowance of 2 mm. the design stress was obtain at operating temperature (T = 180 oC) Design stress.0 mm should be used. and any incidental loads. a minimum allowance of 2.3
Material selection
Carbon steel is chosen because this material mostly used in industry and the prices is cheapest. it is routinely used for most organic chemicals and neutral or basic aqueous solutions at moderate temperatures.
From Table 13.6 Minimum wall thickness
This is required to ensure that any vessel is sufficiently rigid to withstand its own weight.2 page 812 Chemical Engineering Volume 6. 3.4
Welded joint efficiency
Joint efficiency was selected to be 1. Welded joint efficiency. The lower joint factor will result in a thicker and heavier vessel.
63
. f s  109 N / mm2
3. or scaling.0
3.5. For carbon steel.0 because this implies that the joint is equally as strong the virgin plate.

08 for vessels with only a few internal fittings Density of vessel material (7750 kg/m3) Mean diameter of vessel =
Di  t 10 . Weight of tubes
Wt  N t  d o  d i L m g
2 2


Wt  128 0.0195 2  0.08 77509.
66
.80.8Dm t  10 3
Where Wv Cv ρm Dm = = = = total weight of shell 1.3538  10 3
Dm  0.0165 2 577509.885kN
ii.3538  10 3 Wv  1884.5.4094m
Wv  1.509kN
3.815  0. 85% magnesia has been the most popular material.9672 N  1.4093.11 Weight of insulation
Material used
=
85% magnesia
Up to about 600oF (315oC). They are covered with cement to seal gaps and finished off with a canvas that is trated for resistance to the weather.1347 N  16. Equivalents are available for situations where asbestos is undesirable.Wv  Cv m Dm g H v  0. Such insulants are applied to the equipment in the form of slabs or blankets which are held in place with support and clips spotwelded to the equipment. It is a mixture of magnesia and asbestos fibers so constructed that about 90% of the total volume is dead air space.81


Wt  16509. A galvanized metal outer cover may be preferred because of its resistance to mechanical damage of the insulation.
3
m
Dm  406  3.

when it is necessary to divide the vessel into sections for transport or maintenance.37 = 2930.
Standard flanges for inlet water Diameter water inlet pipe Standard o.81390. Welding-neck flanges and branch are suitable for extreme service conditions. G = 0.13 Standard flanges
Flanges joints are used for connecting pipes and instruments to vessel.
For the design of this heat exchanger.53  0.6 mm
69
.6842
0. where flange are likely to be subjected to temperature.6098 kg/m3 Flow rate outlet. shear and vibration loads.5850 mm
Pipe size for ammonia outlet (tube) Material of construction = stainless steel Density of ammonia outlet = 0.7367 mm
3. Flanges joint are also used to connect pipe to equipments such as pumps and valves.37
= 287.6842
0.37
= 258.60980. It is because welding-neck flanges have along tapered hub between the flange ring and the welded joint.= 2930.9883 mm
355. Flanged may also be used on the vessel body.53
0.out = 293G 0. The dimensions of welding-neck flanges is chosen base on the nominal pipe size of the nozzle pipe. This gradual transition of the section reduces the discontinuity stresses between the flange and branch and increases the strength of the flange assembly. Flanges range in size from a few millimeters diameter for small pipes to several meters diameter for those used as body or head flanges on vessels.53
0.6842 kg/s Diameter pipe for ammonia outlet (tube).5.d pipe = = 325. They will normally be specified for the connections and nozzles on process equipment. DNH3 . for manholes cover and for removable vessel head when ease of access is required. All dimensions are listed below. welding-neck flanges are used.

6m is taken since it is the smallest value and the maximum weight is not exceeded.4426 kN.55 E 0.190 G 0.vessel for inspection and maintenance. The assembly of baffles and tubes are hold together by support rods and spacers. Type = single segmental Baffle diameter = 0.3 ≈ 13 baffles
71
. The design of saddle depends on the weight of vessel.095 t2 6 t1 5
mm Bolt diamete r 20
Bolt holes 2
3.5. Since heater is a horizontal arrangement.15 Baffles
Baffles are used in the shell to direct the fluid flow across tube and increase the fluid velocity.
The saddle must be designed to withstand he load imposed by the weight of the vessel and its contents.
Vessel diamete r (m) 0. For outer shell diameter. it is improving the rate of heat transfer. Dshell is 0.406 m Nb = = = length of tube / inside diameter shell 5000 / 406 12.6
Maximum weight (kN) 35
Dimension (m) V 0.26 from Coulson & Rochardson’s Volume 6. the dimensions of saddle choose as referred to Figure 13. Baffle cut used to specify the dimensions of a segmental baffle. the total weight is 18. which is the weight of the heater itself.15 C 0. From the value of weight.406m so 0. baffle cut of 20%-25% will be optimum.48 Y 0. The value will give good heat transfer rate without excessive drop.24 J 0. When the fluid velocity increases. saddle support is chosen as the support. From previous calculation of heater weight. The most commonly used type of baffle is the single-segmental baffle. Generally.

to avoid spurious operation during minor process upset. Table Typical design stresses for plate (The appropriate material standards should be consulted for particular grades and plate thicknesses)
73
. with due allowance for any uncertainty involved in predicting vessel wall temperatures.
3.5. the material of
construction of the column is required to be corrosion resistant.3. The design temperature at which the design stress is evaluated is taken as the maximum operating temperature of the material.
The design pressure will be 10% above the operating pressure. In this case stainless steel type 304 is selected.81°C and pressure of 1 atm.5.1
Operating and Design Temperature and Pressure This column operates at temperature of 66.2
Materials of Construction As one of the process material involve is ammonium nitrate.5
ABSORBER
3.

mm = inner diameter of column. Nmm mm4
= second moment of area of the vessel about the plane of bending
= outer diameter of column. mm
The resultant longitudinal stress:
σw is compressive and therefore negative
As no torsional shear stress. the principal stresses will be σz and σh The radial stress is negligible ≈ (Pi/2) = 0.0507 N/mm2 The greatest difference between the principal stresses will be on the downwind side = σh – σz (downwind)
79
.Bending stress:
Where Mx Iv Do Di
= bending moment at bottom tangent line.